Correct element?

[Barry959]

Have a 38 gallon water heater tank connected to a 30 amp breaker with 10 gauge wire. I went to change the elements and found that they were 3500 208 which I didn't expect. I was planning to put in 4500 240 but now I'm second guessing myself and wondering if I should stick with the original element size. Don't understand why 4500 240 element was not used in the first place. Any thoughts on what element I should use?

 

[Phog]

Some electrical systems are wired as 208V 3-phase. This isn't that common in homes (some people do have it) but it can often be found in commercial or industrial settings. It allows a branch circuit to serve 3 independent 120V loads on a single 4-conductor cable.

The water heater with the 208V rated element is made for use on the 208V type of electrical supply system. Hooking a 208V rated element up to a 240V operating voltage will overdrive the element at roughly 4000W.

I haven't heard that this is a major problem to do. But in theory it could shorten the life of the element. Also many electric water heaters are rated for both voltages, you could check your manual. Perhaps it lists this specifically as being ok to do.

Either way, assuming you have a standard 120V/240V home electrical system, a 240V rated element is the thing to install. Whether you choose a 3500W/240V element (3500W heat dissipation is what the tank is designed and rated for) or go with an oversize 4000W or 4500W one, is between you and your tank. I'm a "run it the way the manufacturer intended" kind of guy, but opinions differ.

 

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[Jadnashua]

A 4500W element used on 240-vac means it will be drawing 18.75A. Since a WH could be running nearly constantly if there is lots of hot water usage, the 80% rule would apply, so that means the circuit should be at least 23.44A. So, your wiring is adequate to handle that higher wattage element. BUT, you have to look at the data plate to see what the maximum design power draw is. It is fairly common for the internal wiring to be smaller than the external stuff, and then that becomes the limiting factor, not the main supply line.

 

[Phog]

A 4500W element used on 240-vac means it will be drawing 18.75A. Since a WH could be running nearly constantly if there is lots of hot water usage, the 80% rule would apply, so that means the circuit should be at least 23.44A. So, your wiring is adequate to handle that higher wattage element. BUT, you have to look at the data plate to see what the maximum design power draw is. It is fairly common for the internal wiring to be smaller than the external stuff, and then that becomes the limiting factor, not the main supply line.

There is also the matter of heat dissipation, inside the tank there are engineered dimensions and materials based on a 3500W heat element. However ASME boiler code usually specifies a 3x or greater safety factor on everything mechanical and most design of such units (whether a feature subject to specific code section or not) is typically undertaken with similar margin in mind. So it's unlikely that a 40% oversized heater element will be an issue. But, this is not an endorsement of putting in oversize elements, only the manufacturer could give that.

 

[WorthFlorida]

With a 38 gallon tank is probably a short. With 3500 watt element water heaters were designed for manufactured homes. Most older "mobile homes" as they were called, always went the cheap way. A 3500 watt unit will allow 12 gauge wire with a 20 amp breaker. There are thousands of old homes that do not have 10 gauge/30a circuits, therefore, 3500 watt elements are changed out for 4500 watt at installation or water heaters are sold with 3500 watt elements. The thermostats are the same.

The internal wiring, as jadnashua stated, is smaller but I'm sure it's the same size wire for 4500 & 3500 water heaters. There is always the possibility that the elements can be upgraded to 4500 watt since the thread size are identical. External wiring is regulated by NEC, internal wiring and components are designed to ANSI standards and for a UL label.

What Phog is stating is true but for electric water heaters there is no heat design rating difference. That is the elements are immersed in water. Nearly 100% of the energy is absorbed by the water. When the water reaches the set temperature, the thermostats turn off the power, therefore, the water doesn't get any hotter than with 3500w or 4500w. The difference is how fast the water is heated to the set temperature. If this was a gas fired heater, than what Phog stated is absolutely true.

I see no problem replacing the elements with 4500 watt as long as you have 10 gauge, 30 a circuit. A hint here is the previous owner may have bought the unit at a good price, less than a 40 gal with 4500 elements and not knowing there was a difference.

 

[Barry959]

Some electrical systems are wired as 208V 3-phase. This isn't that common in homes (some people do have it) but it can often be found in commercial or industrial settings. It allows a branch circuit to serve 3 independent 120V loads on a single 4-conductor cable.

The water heater with the 208V rated element is made for use on the 208V type of electrical supply system. Hooking a 208V rated element up to a 240V operating voltage will overdrive the element at roughly 4000W.

I haven't heard that this is a major problem to do. But in theory it could shorten the life of the element. Also many electric water heaters are rated for both voltages, you could check your manual. Perhaps it lists this specifically as being ok to do.

Either way, assuming you have a standard 120V/240V home electrical system, a 240V rated element is the thing to install. Whether you choose a 3500W/240V element (3500W heat dissipation is what the tank is designed and rated for) or go with an oversize 4000W or 4500W one, is between you and your tank. I'm a "run it the way the manufacturer intended" kind of guy, but opinions differ.

Thanks...your post was helpful

 

[Jadnashua]

If the data plate on the WH allows a 4500W element, it would both work and be according to code requirements. It probably will. To make a real low-end device, though, the internal wiring might not support the higher current ratings. It will tell you either on the data plate or the specs for the unit.

 

[ImOld]

If this is a tank you inherited from someone else, they probably bought the wrong ones and didn't notice or care. Seen it many times. Just install the correct elements and enjoy your hotter water.

 

[Reach4]

The 3500 208 volt element may put out more watts than the 4500 watt 240 volt element, if they are both powered by 240 volts. It could go either way, but I expect they would be similar.

So if your current element has failed, that is one thing. But if you were thinking changing a working element will get your water hot faster, don't count on it.

Basis for the claim? The 3500 208 element has about 12.36 ohm resistance at its rating. The 4500 watt 240 is 12.8 ohm. However if the 3500 208 element runs significantly hotter than at its rated voltage, the resistance would rise. So they would be close.

Power = (V*V)/R or P= V^2/R

So how did a 208 element get put there in the first place? I have a couple of good speculations on that.

 

[hj]

Most element ARE rated 4500/240----3600/208. There is no problem installing a 4500 watt element. If the power IS 208 it will just derate itself to the lower wattage, OR you can install a 5500/240 element and get closer to he 4500/208 capacity. The data plate indicates how the heater was ordered and delivered, NOT what its potential is.